1. Field of Endeavor
The present invention relates to the removal of carbon dioxide from a fluid through the use of tethered catalysts, which optimize the catalyst location for more efficient carbon dioxide removal.
2. State of Technology
The article “Carbon Dioxide into the Briny Deep” in the December 2010 issue of Science and Technology Review provides the state of technology information quoted below and is incorporated herein in its entirety for all purposes.                “WITH every passing year, the amount of carbon dioxide (CO2) in the atmosphere increases. Because of the way this gas absorbs and emits infrared radiation, excessive quantities can cause the warming of Earth's atmosphere. Natural sources of atmospheric CO2 such as volcanic outgassing, the combustion of organic matter, and the respiration processes of living aerobic organisms are nearly balanced by physical and biological processes that remove the gas from the atmosphere. For example, some CO2 dissolves in seawater, and plants remove some by photosynthesis.”        “However, problems arise with the increased amounts of CO2 from human activities, such as burning fossil fuels for heating, power generation, and transport as well as some industrial processes. Natural processes are too slow to remove these anthropogenic amounts from the atmosphere. In 2008, 8.67 gigatons of carbon (31.8 gigatons of CO2) were released worldwide from burning fossil fuels, compared with 6.14 gigatons in 1990.        The present level of atmospheric CO, is higher than at any time during the last 800,000 years and likely is higher than it has been in the last 20 million years. Researchers around the world are exploring ways to dispose of this excess. One proposed approach, called carbon capture and sequestration, is to store CO2 by injecting it deep into the ocean or into rock formations far underground. The G8, an informal group of economic powers including the U.S., has endorsed efforts to demonstrate carbon capture and sequestration. The international forum recommended that work begin on at least 20 industrial-scale CO2 sequestration projects, with the goal of broadly deploying the technology by 2020.”        “Several carbon sequestration projects are already under way. One, under the North Sea, is part of an oil drilling operation that separates CO2 from natural gas and traps it in undersea rock formations. Other projects are using sequestered CO2 to push oil around underground so that drillers can maximize the quantity of crude oil they remove a process called enhanced oil recovery.”        “An alternative approach, being pursued by researchers at Lawrence Livermore and the Department of Energy's National Energy Technology Laboratory, involves putting CO2 back into the ground while simultaneously producing freshwater. According to Livermore geochemist Roger Aines, who leads the Laboratory's work on this project, vast underground sandstone formations are filled with very salty water, many times saltier than the ocean. The idea is to pump CO2 into these rock formations, thereby pushing briny water up into a reverse-osmosis water-treatment plant where most of the salt can be removed. The result is to increase volume for storing CO2 in the underground formation while producing freshwater aboveground.”        “Although this water might be too salty to drink, it would provide a critical resource for industrial processes that require huge quantities of freshwater. Petroleum refining, for example, consumes 1 to 2 billion gallons of water per day. Even technologies designed to reduce greenhouse gases, such as the biofuels production process, are increasing demands on the world's water resources.”        
The article “From Respiration to Carbon Capture,” by Katie Walter of the Lawrence Livermore National Laboratory, in the March 2011 issue of Science & Technology Review, pages 4-9, provides the state of technology information quoted below and the disclosure of this article is incorporated herein in its entirety for all purposes.                “Our lungs separate, capture, and transport carbon dioxide (CO2) out of blood and other tissues as part of the normal respiration process. The catalyst that initiates this natural response in the lungs is carbonic anhydrase, the fastest operating natural enzyme known.”        “Other enzymes play an “energy” role in our bodies as well. For example, ribulose-1,5-bisphosphate carboxylase oxygenase, more commonly known as RuBisCO, catalyzes the first major step of carbon fixation. In that process, molecules of atmospheric CO2 are made available to organisms in the form of energy-rich molecules such as glucose. Methane monooxygenase, or MMO, oxidizes the carbon-hydrogen bond in methane.”        “Medical researchers have used these enzymes as guides for designing synthetic catalysts that speed up chemical reactions. Now, a collaboration led by Lawrence Livermore is examining carbonic anhydrase as the basis for a new molecule that does for coal-fired power plants what the enzyme does for our bodies: quickly separate CO2. But instead of transporting it out of blood or tissue, the catalyst will remove the greenhouse gas before a power plant emits it to the atmosphere.”        “Developing a synthetic molecule to replace CO2 scrubbing processes that use amines could greatly speed up carbon capture,” says geochemist Roger Aines, the principal investigator for the catalyst project. “Current analysis indicates that efficient catalysts might increase the capture rate for CO2 separation by as much as 1,000 times.”        “The ARPA-E team is examining two possible molecular designs. One is a relatively simple dissolved catalyst system that could be applied immediately in industrial practice. This technology, known as regenerable solvent absorption technology, or RAST, is being developed largely by Babcock & Wilcox. The second, a Livermore design, is a “tethered” molecule that holds the catalyst at the air-liquid interface where the CO2 transfer typically takes place. The tethered molecule looks much like mosquito larvae floating just below the surface of water. This approach promises very high efficiency, but using it in power plants may require changes in industrial practices.”        “Several challenges remain to make the synthetic catalysts suitable for a commercial CO2 capture process. First, the molecular scaffolding must be structurally stable to preserve the metal ion in the catalytic pocket under high temperatures and pressures.”        “Addressing structural robustness and fast catalytic rates would normally be a slow, expensive process. Because of Livermore's computational and synthetic chemistry capabilities, the ARPA-E team can quickly evaluate hundreds of candidate compounds computationally, synthesize dozens, and test the most promising ones in the laboratory. Aines estimates that in just two years, the team will be ready to conduct long-term stability experiments on candidate molecules in large-scale testing facilities.”        “In addition, catalysts for the tethered molecule design must remain within about 100 micrometers of the gas-water interface, where they are most effective. If the catalyst is distributed throughout the solvent, more of it must be produced overall. The team is investigating an approach that adds a hydrophobic molecule to tether the molecule at the gas-water interface. Livermore's preliminary calculations show that such tethers do not deform the catalyst and should preserve full functionality. Another design possibility uses very small particles containing the catalyst on their surface. These particles move with the solvent and can be easily extracted before thermal desorption.”        “As candidate molecules move closer to commercialization, team members at Livermore and Babcock & Wilcox will work together to balance the cost of catalyst production with the molecule's expected lifetime. “For now, we are estimating that a catalyst will live at least a few days, possibly longer,” says Aines. “Surviving the high temperature is the greatest challenge in designing an effective catalyst and will be the limiting factor with this technology.”        
States Published Patent Application No. 2007/0169625 by Roger D. Aines and William L. Bourcier for a carbon ion pump for removal of carbon dioxide from combustion gas and other gas mixtures published Jul. 26, 2007 provides the state of technology information quoted below. The disclosure of United States Published Patent Application No. 2007/0169625 is incorporated herein in its entirety for all purposes.                “A major limitation to reducing greenhouse gases in the atmosphere is the expense of stripping carbon dioxide from other combustion gases. Without a cost-effective means of accomplishing this, the world's hydrocarbon resources, if used, will continue to contribute carbon dioxide to the atmosphere.”        “A few major power plants around the world currently remove carbon dioxide from flue gas, for sale as an industrial product. Oil companies commonly remove carbon dioxide from natural gas to improve its energy content. In both cases the most common technology is temperature-swing absorption (TSA) using a methylated ethyl amine solvent (MEA).”        “The MEA process relies on the strongly selective bonding of carbon dioxide to the solvent for selective removal from the flue gas, but requires considerable heating to increase the gas pressure in the removal step to an acceptable level. In particular, the flue gas contacts the MEA dissolved in water in a packed column, and then the carbonated solution is heated to 120° C. to extract a nearly pure carbon dioxide gas. Sulfur and nitrous oxide are removed ahead of this step because they bind so tightly to the solvent that they cannot be removed. An alternative MEA cycle using pressure cycling can be used in some cases, when the inlet gas to be separated is at high pressure and the carbon dioxide can be removed from the solvent by lowering the ambient pressure. In both this process and the temperature swing process, the carbon dioxide fugacity is changed by changing the physical conditions of the solvent. This is inefficient due to the energy unrecoverably lost doing work on a large volume of solvent, in addition to the mechanically complex system and the need for frequent solvent addition due to degradation. It is a fundamentally complex and chemically-intensive process only suitable for large-scale industrial separation today and it is too expensive to contribute a globally-large removal of carbon from combustion sources.”        “The Greenhouse Gas Program of the International Energy Agency (Davison et al. 2001) has studied the application of this technology to electric power plants. They estimate an energy cost of approximately 35% of the power generated by a pulverized coal power plant is required for this type of carbon dioxide removal. Many variants are under study, which permit slightly higher efficiency or longer solvent life, including solid sorbents; thus far, dramatic improvements have not been seen.”        “Accordingly, a need exists for an improved process and system to control the removal of CO, in an economical and environmentally safe way. The present invention is directed to such a need.”        